A device of this type is known (GB-A No. 2094191), in which the tightening bolt is designed as a one-piece connecting bolt, the one end of which can be constructed as an internal cone and the other end of which can be constructed as an external cone. The tightening operation is started in this device by screwing in the retaining screw (tightening screw) provided with an external cone. When, during screwing in of the tightening screw, abutment occurs, then the forces started by the screw occur first on the side of the tightening screw on the tightening bolt. The tightening bolt is thereby first pressed on the side of the tightening screw against the base surface of the crossbore, which base surface faces away from the end of the fitting pin, such that the fitting pin is pulled into the mating bore. This also takes place directly thereafter during an engagement of the external cone on the tightening bolt with the internal cone on the oppositely positioned retaining screw. As soon as a specific tightening action exists, a complete change of the radial forces into an axial component occurs causing a pressing of the annular end face of the fitting pin and the ringlike end face of the connecting sleeve against one another. This type of tightening results preferably in a reinforcement of the connecting device in direction of the tightening bolt. The torsion forces occurring during a machining operation cause an abutting of the internal and external cones which are adjacent to one another, which abutting is made possible mainly by the tightening bolt being able to carry out a small rotation about its own axis. The tightening between the annular end face and the ringlike end face is thus increased and also the connection is enhanced. Furthermore, the abutting effect results in a nonharmonic vibrating behavior in the connecting area with the result that the frequency of the system is shifted in dependency of the torsion moment and a possibly occurring torsional vibration is therefore dampened.
Furthermore it is known in a device of the above type to design the tightening bolt in two parts and to start the tightening operation with a sliding cam arranged between the two tightening-bolt parts and axially operable through a feeding device arranged on the side of the machine (V-drive). A tightening of the tightening bolts provided with an external cone and of the retaining screws provided with an internal cone and arranged in internally threaded openings of the connecting sleeve takes here also place during the tightening operation. The connecting device is reinforced here also preferably in direction of the tightening bolts.
The basic purpose of the invention is to improve the connecting device of the above-disclosed type, such that the stiffness or rigidity transversely to the tightening-bolt axis is increased, and the changing precision and the damping behavior are improved.
The invention is based on the thought that a four-point contact is provided between the fitting pin and the mating bore in two directions which are perpendicular to one another, as well as an alignment, which is exactly centered taking into consideration the movability of the tightening bolt, and thus a high degree of changing precision is guaranteed. In addition, a reinforcement of the connecting device in two bending directions, which are perpendicular to one another, results.
In order to achieve this, it is suggested, according to a first embodiment of the invention, that the connecting sleeve be widened elastically in axial direction of the tightening bolt during the tightening operation such that it is pressed in transverse direction hereto during an elastic diameter reduction in diametrically opposed areas with the inner surface of the mating bore against the outer surface of the fitting pin. By suitably selecting the wall thicknesses and the external and internal tolerances of the fitting pin and of the mating bore, a four-point contact is thus obtained with the above-described advantages of an increased stiffness transversely with respect to the tightening-bolt direction and an improved self-centering and changing preciseness. This effect furthermore improves the vibrating behavior of the connecting system during bending and torsional vibrations.
Alternatively and in connection with the above solution characteristics, it is suggested according to a further embodiment of the invention that the crossbore provided in the fitting pin have a recess in the area of its base surface facing away from the end of the pin, which recess extends over the length of the crossbore and forms at its longitudinal edges a contact surface for the tightened-in tightening bolt. It is achieved with this measure that the fitting pin during the tightening operation does not rest on the base surface facing away from the end of the pin but on two contact lines on the surface of the crossbore, which contact lines are laterally offset with respect to the base surface of the bore. A radial force component is in this manner during the tightening operation applied by the tightening bolt, aside from the force component acting in axial direction of the fitting pin, onto the fitting pin, which radial force component radially elastically widens the fitting pin by some microns (.mu.'s). This widening bridges the clearance transversely with respect to the tightening-bolt direction and thus results also in a self-centering four-point contact with the above-discussed advantages. In addition, the possibly disadvantageous elastic deformation of the connecting sleeve is at least partly reversed or becomes unnecessary.
According to an advantageous further development of the invention, the recess is formed by a bore, which is eccentric in a direction toward the end of the pin compared with the crossbore and which has a smaller diameter compared with the crossbore. It is basically also possible to form the recess through an oval deformation of the crossbore, which oval deformation is elongated toward the end of the pin.
It has been proven to be particularly advantageous when the edges of the recess around the axis of the crossbore define an angle of .+-.40.degree. to .+-.50.degree. with respect to the sides of the base surface of the bore.
A further advantage of this measure is that the tightening bolt experiences an additional tightening and reinforcement within the crossbore so that an improved torque transfer during the machining operation is guaranteed.
Alternatively and in connection with the above solution measures, it is suggested according to the invention that the fitting pin has a notch extending over the length of the crossbore, which notch opens toward the inside of the crossbore. The notch can thereby be arranged in the area of the base surface of the crossbore which faces away from the free end of the pin and/or the root of the pin. This notch results during the tightening operation in an expansion of the crossbore and thus in an enhanced bulging of the fitting pin and in the desired self-centering of the four-point contact. The depth of the notch should thereby be a multiple of the wall thickness between the base of the notch and the end of the pin. If necessary, the notch can also be designed as a slot going through to the end of the pin. The width of the notch should be chosen as small as possible. In order to avoid accumulations of dirt in the notch area, the notch can be filled with an elastomer material.